With rapid development of integrated circuit (IC) technology, semiconductor devices, such as MOS (metal oxide semiconductor) devices, in the integrated circuits continue to shrink to provide micromation and integration.
For transistors, as the sizes continue to shrink, when using silicon oxide or silicon oxynitride materials for forming a gate dielectric layer, the formed devices are unable to meet the performance requirements for the transistors. In particular, transistors formed using silicon oxide or silicon oxynitride as the gate dielectric layer may easy to generate leakage current and cause impurity diffusion issues, which affect the threshold voltage of the transistor and decrease reliability and stability of the formed transistors.
To solve the above problems, a transistor may be formed to include a high-K gate dielectric layer and a metal gate. This transistor is also called a high-K metal gate (HKMG) transistor. The HKMG transistors use high-K (high dielectric constant) materials to replace silicon oxide or silicon oxynitride to form the gate dielectric material, and use a metal material or metallic compound material to replace polysilicon gate material to form the metal gate. With reduced sizes, the HKMG transistors may be able to reduce: leakage current, and the operating voltage and power consumption, and to improve performance of the transistors.
However, the HKMG transistors formed by such a gate-last process may have poor morphologies and undesirable performance.